Wireless communications develop continuously. New communication systems entail and others may disappear. During the 4G era, various communication systems such as GSM (Global System for Mobile Communications), CDMA (Code Division Multiple Access), CDMA2000, WCDMA (Wideband CDMA), UMTS (Universal Mobile Telecommunications System), HSPA (High Speed Packet Access), WiFi (Wireless Fidelity) and W-LAN (Wireless Local Area Network), UWB (Ultra Wideband), WiMAX (Worldwide Interoperability for Microwave Access), LTE (Long Term Evolution) or UTRA (Universal Terrestrial Radio Access) and LTE-Advanced or E-UTRA (Evolved UTRA) network technologies may co-exist and at least some of them potentially be accessible by a dual- or multi-mode terminal or handset. Capability of handing over traffic efficiently between heterogeneous access technologies is then expected to be of particular significance for providers of communication services.
Cellular wireless communications systems provide a means of covering a surface with wireless communications resources. A surface to be covered by wireless services is divided into a number of smaller areas, cells, each cell being served by one or more base stations. With a great number of base stations, BSes, each base station providing services for a corresponding cell of service coverage, a great surface is covered. In e.g. UMTS and UTRA; the logical concept or representation of a base station is referred to as Node B; and in E-UTRA, E-UTRAN Node B or eNB. In WiMAX, it is referred to as enhanced base station. In case a wireless resource such as radio frequency spectrum is used repeatedly in more than one cell, a great service area can be covered also with a limited amount of the wireless resource.
A surface covering system need keep track of a terminal or handset for communications over the system, subsequently and correspondingly referred to as an MS (Mobile Station) or SS (Subscriber Station), a UED (User Equipment Device) or UE (User Equipment), to be capable of connecting a call or delivering arriving data destined for it or its user. The tracking of circuit switched, CS, traffic and packet switched, PS, traffic need not be the same.
Considering a system providing CS services over GSM and PS services over GPRS using GSM radio technology as an example, there are a location area identifier, LAI, and a location area code, LAC, for the CS services and a routing area identifier, RAI, and routing area code, RAC, for the PS services broadcast from the base stations in a repeating cycle.
International Patent Application WO2007113457, provides a mobile terminal with system information which enables the terminal to access one of the cells of a cellular telecommunications system. The network includes an HLR/HSS (Home Location Register/Home Subscriber Server) which, for each subscriber of the network, stores the IMSI (International Mobile Subscriber Identity) and the corresponding MSISDN (Integrated Services Digital Network) number together with other subscriber data, such as the current or last known location of the subscriber's mobile terminal.
Conventionally, the base stations are arranged in groups and each group of base stations is controlled by one MSC (Mobile Switching Centre). MSCs support communications in the circuit switched domain—typically voice calls. Corresponding SGSNs (Serving GPRS Support Nodes) are provided to support communications in the packet switched domain—such as GPRS (General Packet Radio Services) data transmissions. The MSC stores subscriber data temporarily in a location in a VLR (Visitor Location Register). In this way, therefore the particular subscriber is effectively registered with a particular MSC, and the subscriber's information is temporarily stored in the VLR associated with that MSC. The information stored on the VLR includes a TMSI (Temporary Mobile Subscriber Identification) number for identification purposes for the terminal within the MSC. The TMSI number is an identification number that is typically 32 bits in length. In conventional systems, therefore, the TMSI number is not allocated to more than one user of a given system served by that MSC at one time. Consequently, the TMSI number is usually invalidated when the mobile station crosses into a new location served by a different MSC. The SGSNs function in an analogous way to the MSCs. The SGSNs are equipped with an equivalent to the VLR for the packet switched domain.
When the HLR (Home Location Register) is interrogated by the MSC, the HLR additionally performs an authentication procedure for the mobile terminal. If the mobile terminal is deemed authenticated, the MSC requests subscription data from the HLR. The HLR then passes the subscription data to the VLR.
When a mobile terminal is in an inactive or idle state, when a calling party (whether a subscriber within the mobile telecommunications network or outside it) attempts to call a mobile terminal within the network, that mobile terminal must be paged. Paging is a process of broadcasting a message which alerts a specific mobile terminal to take some action; for paging, to notify the terminal that there is an incoming call to be received. If the network has information on the cell where the mobile terminal is located, it is only necessary to page in that cell. However, if the mobile terminal is moving within the network, the precise cell in which the mobile terminal is located may not be known. It will therefore be necessary to perform paging in a number of cells. The greater the number of cells in which paging must occur, the more use of valuable signaling capacity within the network.
However, typically the area covered by a single MSC and SGSN is large, and to page all the cells covered by a single MSC and SGSN would require a significant amount of paging signaling.
The problems of excessive use of signaling capacity by paging a multiplicity of cells or performing a multiplicity of frequent location updates is solved in 2G and 3G networks by dividing the coverage area of the mobile telecommunications network into a plurality of paging areas, referred to as location areas, LAs, or routing areas, RAs.
A location area relates to a particular geographical area for communications in the circuit switched domain. Typically, although not necessarily, a location area is larger than the area of a single cell but is smaller than the area covered by one MSC. Each cell within the network broadcasts data, LAI, indicative of the identity of its location area. The mobile terminal uses this data to determine when it has moved into a new location area. The terminal stores its last known location area on its SIM. This information stored on the SIM is compared with the location area information broadcast by the local cell. The identities of the two location areas are compared. If they are different, the mobile terminal determines that it has entered a new location area. The mobile terminal then gains access to a radio channel and requests a location area update, LAU. The request includes LAI of the earlier/old location area and the terminal's current TMSI. If the MSC/VLR is the same for the new and old location areas, the network can immediately authenticate the mobile terminal and note the change of location area. However, if the mobile terminal has moved to a different MSC/VLR, the MSC/VLR addresses a message to the HSS/HLR. The HSS/HLR notes the new location and downloads security parameters to allow the network to authenticate the mobile. It also passes on subscription details of the user to the new VLR and informs the old VLR to delete its records. The new MSC/VLR allocates a new TMSI to the mobile.
A routing area relates to a particular geographical area for communications in the packet-switched domain. Typically, although not necessarily, a routing area is larger than the area of a single cell but is smaller than the area covered by one SGSN. A routing area is typically, although not necessarily, smaller than a location area. There may be many routing areas within one location area. Each cell within the network broadcasts data indicative of its routing area in addition to the data mentioned above indicative of the identity of its location area. The mobile terminal uses this received data to determine when it has moved to a new routing area. The terminal stores the last known routing area on its SIM. The information stored on the SIM is compared with the routing area information broadcast by the local cell. The identities of the two routing areas are compared. If they are different, the mobile terminal determines that it has entered a new routing area. The mobile terminal then gains access to a radio channel and requests a routing area update, RAU. The routing area is updated correspondingly to the location area, as discussed above.
As mentioned above, GSM and UMTS mobile telecommunications networks are divided into paging areas (location areas/routing areas). The LTE network has the equivalent of location/routing areas (herein “tracking areas”, TAs). Tracking area updates are performed similar to RAUs and LAUs.
In WO2007113457, a minimum set of system information is transmitted by eNodeB (evolved Node-B) of the base station that serves the cell in which the mobile terminal is located. This system information minimum set only includes a sub-set of the information that is conventionally transmitted on the BCH. The system information minimum set includes an identifier of the network, PLMN ID, and tracking area, TA, in which the cell is located, as well as information to find the RACH and to configure access to the RACH.
The system information indicator of WO2007113457 directs the mobile terminal to retrieve the system information from a store and use the system information to access the telecommunications system. This store is a store on the mobile terminal which stores a plurality of respective system data. The system information indicator received on the BCH directs the mobile terminal to retrieve and use a particular one of the stored system data. It is not necessary, therefore, for all the system data to be transmitted by the telecommunication system to the mobile terminal. How ever, these system data can be transmitted by the telecommunications system when desired; for example, in order to update the system data. Generally, however, this updating will not be performed using the BCH. The system data stored on the mobile terminal may be pre-stored thereon when the mobile terminal is manufactured.
In e.g. WiMAX, usually plural cells are, similar to WO2007113457, grouped into a PA (Paging Area) or PG (Paging Group) for paging of mobile stations. An MS receiving the location area and routing area information may thereby detect an area code change when its user moves across paging area borders.
3rd Generation Partnership Project, Technical Specification Group GSM/EDGE Radio Access Network, ‘Multiplexing and multiple access on the radio path,’ 3GPP TS 45.002 V7.7.0, France, May 2008, describes transmission of system information in a multi-frame structure. E.g. system information type 13, SI13, is related to GPRS. An SI13 message is sent on a normal broadcast control channel, BCCH Norm, or a BCCH Ext, an additional downlink channel obtained by taking away blocks normally used for paging/access grant. In the case that the message is sent on the BCCH Norm, it is sent at least once within any of 4 consecutive occurrences of TC=4. If sent on BCCH Ext, it is sent at least once within any of 4 consecutive occurrences of TC=5. The type code, TC, is a sequence number within a multi-frame comprising 52 frames.
3rd Generation Partnership Project, Technical Specification Group Core Network and Terminals, ‘Numbering, addressing and identification,’ 3GPP TS 23.003 V8.3.0, France, December 2008, defines assigning principles and identification plans. In section 4.3, it illustrates CGI (Cell Global Identification), see FIG. 1, and BSIC (Base Station Identify Code). CGI comprises MCC (Mobile Country Code) identifying the country in which the PLMN (Public Land-Mobile Network) is located, MNC (Mobile Network Code) identifying PLMN in that country, LAC (Location Area Code) identifying a location area within a PLMN and CI (Cell Identity). RAC occupies 1 octet and LAC occupies 2 octets. The 3GPP specification also mentions a TAC occupying 16 bits.
International Patent Application WO2004054286A2, describes a GSM for seamless operation with WCDMA networks. Additional capabilities are defined for GSM and specified in Release 99 version of the GSM standard. One of these additional capabilities is the ability for a GSM network to broadcast information for neighboring WCDMA cells. This broadcast information allows dual-mode terminals operating on the GSM network to learn of the presence of WCDMA cells. Moreover, the broadcast information includes cell-specific information that may be used by the dual-mode terminals to quickly acquire the WCDMA cells. Such cell-specific information includes, for each WCDMA cell, (1) the frequency and primary scrambling code used by the WCDMA cell and (2) whether or not diversity mode is employed by the WCDMA cell. WCDMA and GSM each provides a “cell reselection” process whereby a terminal operating on one network determines a suitable cell in another network from which it plans to receive available services.
3rd Generation Partnership Project, Technical Specification Group Radio Access Network, ‘Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN),’ 3GPP TS 36.300 V8.7.0, France, December 2008, describes an ANR (Automatic Neighbor Relation) function relying upon cells broadcasting their identity on a global level, ECGI (E-UTRAN Cell Global Identifier). For inter-RAT and inter-Frequency ANR, each cell contains an Inter Frequency Search list. This list contains all frequencies that shall be searched. During connected mode, an eNB can instruct a UE device to perform measurements and detect cells on other RATs/frequencies. FIG. 3 illustrates schematically the inter-RAT/inter-frequency ANR function in case of a UTRAN detected cell (307). Anticipating a base station (302) operating according to UTRAN access technology and providing radio coverage over a cell (307), a base station (301) operating according to E-UTRAN or LTE access technology and providing radio coverage over a cell (306), and a UE device (303) capable of operating according to both E-UTRAN and UTRAN access technologies, the eNB (301) first instructs (311) the UE device (303) to look for neighbor cells (307) in the target RATs/frequencies. To do so, the eNB (301) may need to schedule appropriate idle periods to allow the UE device (303) to scan broadcast channels of all cells in the target RATs/frequencies. Second, the UE device (303) reports (312) PCI (Physical Cell-ID) of the detected cells (302, 307) in the target RATs/frequencies. A reserved range of PCI is only applicable to the frequency of the PLMN where the UE device received it. The PCI is defined by
the carrier frequency and PSC (Primary Scrambling Code) in case of UTRAN FDD (Frequency Division Duplex) cell,
the carrier frequency and the cell parameter ID in case of UTRAN TDD (Time Division Duplex) cell, and
the Band Indicator+BSIC (Base Station Identity Code)+BCCH ARFCN (Absolute Radio Frequency Channel Number) in case of GERAN cell.
Third, when the eNB (301) receives (312) a report from the UE device (303), the eNB (301) instructs (313) the UE device (303), using the newly discovered PCI as parameter, to read (314)
ECGI, TAC (Tracking Area Code) and all available PLMN ID(s) of an inter-frequency detected cell,
CGI (Cell Global Identity), LAC (Location Area Code) and RAC (Routing Area Code), in case of a UTRAN inter-RAT detected cell, and
CGI and RAC of the detected neighbor cell, in case of a GERAN inter-RAT detected cell.
ECGI (E-UTRAN Cell Global Identifier) is constructed from the MCC (Mobile Country Code), MNC (Mobile Network Code) and the ECI (E-UTRAN Cell Identifier). The ECI is used to identify cells within a PLMN. ECI has a length of 28 bits and contains the eNB Identifier. The eNB Identifier is either of short length, 20 bits, which allows addressing of up to 256 cells per eNB (identifier) or of long length, 28 bits, which allows addressing of one cell per eNB. The UE device (303) ignores transmissions (313) from the serving cell 301 while finding the requested information transmitted in the broadcast channel of the detected inter-system/inter-frequency neighbor cell (302). For this purpose, the eNB (301) may need to schedule appropriate idle periods to allow the UE to read (314) the requested information from the broadcast channels of the detected inter-system/inter-frequency neighbor cells (302). Finally, the UE device (303) reports (315) detected parameters CGI, ECGI, LAC, RAC, TAC and PLMN-ID(s) as applicable.
International Patent Application WO2008054668, describes LTE tracking area updates, TAUs, and TAC (Tracking Area Code) and PLMN-ID (Public Land Mobile Network Identification) assisted optimized WTRU (Wireless Transmit/Receive Unit) cell reselection. An evolved Node-B broadcasts system information including at least one SIB (System Information Block) based at least in part on an E-UTRAN parameter response message sent by an EPC (Evolved Packet Core) network. A WTRU generates a new TAC, which represents a tracking area identification, TA-ID, of a new cell, based on the system information, and compares the new TAC to an existing TAC, which represents a TA-ID of a previous cell. The WTRU transmits to the EPC network a TAU request message including the TA-ID of the new cell. The EPC network sends either a TAU accept message or a TAU reject message to the WTRU. Example globally unique TAC is identical to TA-ID. Another example TA-ID equals the sum of PLMN-ID and TAC. Up to 24 bits are provided for TA-ID and TAC. FIG. 2 illustrates an example TA-ID information element, where each row corresponds to an octet. There are three optional octets for MCC and MNC (201-206), two mandatory TAC octets (207, 208) and one optional TAC octet (209). In the example TA-ID, there is also additional mandatory field (210) included. The fields for MCC and MNC (201-206) correspond to PLMN-ID.
International Patent Application WO2007089556, discloses a wireless communication method and system for performing dual mode paging for multi-mode terminal operation in that system. The wireless communication system includes an E-UTRAN, a 2G/3G RAN (Radio Access Network) and at least one WTRU including an EE (Evolved Element) in communication with the E-UTRAN and a 2G/3G element in communication with the 2G/3G RAN. The WTRU is reachable in the LTE system while registered in 2G/3G system, and vice versa. The system may first attempt paging the WTRU over a 2G/3G RAN, and then attempt a second page on an LTE RAN. If the WTRU receives a first page message via the 2G/3G RAN, then it may respond on the 2G/3G RAN. If the WTRU did not receive the first page because it is camping on the LTE side, then it receives the second page message via the E-UTRAN. The WTRU responds to the second page message via the EE.
International Patent Application WO2008025502A1 describes a method to balance traffic load between nearby cells and to optimize the use of radio resources in loaded WiMAX profile C and LTE environments, in which a central RRM (Radio Resource Management) function is not available. Nearby cells are grouped into constellations. Load status information is exchanged within the constellation for achieving RRM optimizations in a distributed environment in which no central RRM controller exists. In particular, cell traffic load balancing should be achieved by exchanging radio resource utilization information between base stations and by offloading busy cells via standard handover, HO, procedures, in order to prevent flooding situations. Border constellation cells are enabled to trigger traffic offloading only when the average actual traffic load of the neighbor constellation is lower than its target utilization parameter. RAN structure in which the functions of the centralized controller, e.g. the RNCs in UTRAN, are partially shifted to the base stations in order to reduce latencies and improve the quality of service, QoS, provided to the end user. Both architectures allow BS-to-BS communication for coordination purposes. LTE systems provide this via a specific interface, X2, between eNBs, while WiMAX may rely on the availability of a mediation function provided by a central controller, ASN-GW (Access Service Network Gateway) or a logic BS-to-BS interface, R8.
Haihong Zheng et al., ‘Inter-RAT mobility in 802.16m,’ IEEE C802.16m-08/647r1, July 2008, propose Inter-RAT handover for some radio access technologies. For W-LAN and WiMAX, mobile stations are always paged over WiMAX. A first alternative for handover between WiMAX and cdma2000 requires dual radios. A second alternative for handover between WiMAX and cdma2000 relies upon broadcast or multicast indication of neighboring target BS supporting cdma2000. After detecting the indication, the dual mode MS may switch on the secondary radio to scan for cdma2000 network based on its PRL (Preferred Roaming List) and other policies defined. The serving BS may also provide the system information of the target BS in the neighbor advertisement, which can be used by MS to access and register with the target BS. The connection with the serving BS is kept alive until the handover completes. Handover between WiMAX and 3GPP radio access technologies not requiring dual radios is also included.